Motor drive device with lock protection function

ABSTRACT

A cooling system is provided with a motor drive device, a fan motor, and a Hall element. The motor drive device includes a lock protection circuit and a lock controller. When a control signal instructing rotation of the fan motor that is to be driven instructs stoppage of the motor for a predetermined time-period or longer, the lock controller has the lock protection circuit inactive. At an occasion when the control signal has continued to instruct stoppage of the fan motor for a first time-period or longer, a standby controller starts time measurement, and after a further predetermined second time-period has elapsed, makes at least a part of the motor drive device transition to a standby mode.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/825,782 filed on 29 Jun. 2010, which is acontinuation application of U.S. patent application Ser. No. 12/101,338,filed on 11 Apr. 2008, the entire contents of each of which areincorporated herein by reference. The 12/101,338 application claimed thebenefit of the date of the earlier filed Japanese Patent Application No.JP 2007-105184 filed 12 Apr. 2007.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to motor drive technology, and inparticular, to a motor drive device provided with a lock protectionfunction, a cooling system using the motor drive device, and a lockprotection method.

2. Description of the Related Art

With the speeding up of personal computers and workstations in recentyears, operation speeds are increasing steadily for computational LSIs(Large Scale Integrated circuits), such as in CPUs (Central ProcessorUnits), DSPs (Digital Signal Processors) and the like. There is aproblem in that heat generated from an LSI leads to thermorunaway of theLSI itself, or has an effect on a surrounding circuit. Therefore,appropriate thermal cooling of the LSI is an extremely importanttechnology.

An example of a technology for cooling the LSI is a cooling method ofair-cooling by a cooling fan. In this method, for example, the coolingfan is installed opposite a front surface of the LSI, and cool air isblown on the LSI front surface by the cooling fan.

In a motor that drives the cooling fan, when the motor is locked by aforeign object being caught in the fan or the like, there is a risk ofdamaging device reliability by an excess current flowing in a coil or asemiconductor device. To tackle this type of problem, a lock protectioncircuit is used which stops energization of a motor coil when rotationof the motor is stopped.

In the technology described in Patent Document 1, when it is detectedthat rotation of a motor is stopped based on output of a rotation sensorthat detects a rotation state of the motor, an automatic reset signal Eis generated until the motor is reset to a rotation state. The automaticreset signal E is, for example, a signal that sequentially repeats an ONstate of approximately 0.5 seconds and an OFF state of approximately 3seconds. That is, when it is detected that rotation of the motor isstopped, after a halt period of approximately 3 seconds an attempt tostart the motor for 0.5 seconds is repeated.

However, in the technology described in Patent Document 1, a lockprotection function operates not only in cases in which the motor islocked, but also when rotation of the motor is stopped by an instructionby a control signal. As a result, when a signal that makes the motorrotate, from outside, is inputted, after operation of the lockprotection function, after this input, until the automatic reset signalE is asserted, the motor cannot be rotated. That is, after the motor hasbeen stopped by an instruction by the control signal, when a temperaturerise of a device to be cooled is detected and the motor restartsrotation, a time lag until the start of rotation occurs, and there is aproblem with temperature management.

Patent Document 1: Japanese Patent Application, Laid Open No. 2005-6405

Patent Document 2: Japanese Patent Application, Laid Open No. H10-234130

SUMMARY OF THE INVENTION

Recognizing this situation, the inventor realized the present invention,and a general purpose thereof is the provision of a motor drive devicethat can promptly restart rotation of a motor, after the motor has beenstopped by an instruction by a control signal, a lock protection method,and a cooling system that makes use thereof.

An embodiment of the invention relates to a motor drive device. Themotor drive device includes: a drive unit which controls energization ofa motor that is to be driven, based on a control signal instructingrotation of the motor; a lock protection circuit which stopsenergization of the motor, when the motor is stopped; a lock controllerwhich has the lock protection circuit inactive, in cases in which thecontrol signal continues to instruct stoppage of the motor for at leasta predetermined first time-period; and a standby controller which startstime measurement at an occasion when the control signal has continued toinstruct stoppage of the motor for at least the first time-period, andafter a further predetermined second time-period has elapsed, stops atleast part of the motor drive device, and makes the motor drive devicetransit to a standby mode.

According to this embodiment, in cases in which the control signalcontinues to instruct stoppage of the motor for at least the firsttime-period, the lock controller has the lock protection circuitinactive, so that it is possible to speed up restarting driving onceagain, after rotation of the motor is stopped by the instruction by thecontrol signal. The control signal may be a pulse width modulationsignal. The control signal may be a signal which adjusts duty ratio ofthis pulse width modulation signal.

Furthermore, after the second time-period has elapsed, since there is atransition to the standby mode, it is possible to realize low powerconsumption, and when there is a transition to the standby mode, sincethe lock protection circuit is inactive, when the motor is instructed todrive thereafter, rotation of the motor can be done speedily.

The standby controller, in the standby mode, may stop a voltage source(starting circuit) which generates a reference voltage for the motordrive device.

The standby controller, in the standby mode, may stop supplying ofvoltage to a Hall element for detecting rotation of the motor. Sincecurrent flowing in the Hall element is relatively large in comparison tocurrent in another circuit block, it is possible to effectively reducepower consumption.

The standby controller, in the standby mode, may fix potential of acontrol terminal of a transistor of an output stage connected to a coilof the motor, to turn the transistor fully OFF.

Since the size of the transistor of the output stage is large, theeffect of reducing power consumption by turning it fully OFF is large.

The standby controller, at an occasion when the control signal instructsdriving of the motor, may reset from the standby mode to normal mode.

The lock controller may be provided with a counter circuit whichmeasures elapsed time from when the control signal instructs stoppage ofthe motor. In such cases, it is possible to accurately measure thepredetermined first time-period.

With regard to the lock protection circuit, a time-period, that isshorter than a verification time-period necessary for confirming thatthe motor has stopped, may be set as the predetermined firsttime-period. In such cases, after the motor has been stopped by aninstruction by the control signal, since the lock protection circuit isinactive before the lock protection function operates, in cases in whichthe motor is driven once again after stoppage of the motor by thecontrol signal, it is possible to promptly restart rotation of themotor.

The motor drive device may be monolithically integrated on onesemiconductor substrate. “monolithically integrated” includes cases inwhich all component elements of the circuit may be formed on thesemiconductor substrate, and cases in which main component elements ofthe circuit are integrated as a unit, and some resistors, capacitors, orthe like, for adjusting a circuit constant may be arranged outside thesemiconductor substrate. By integrating the motor drive device as oneLSI, it is possible to reduce circuit area.

Another embodiment of the present invention is a cooling system. Thesystem is provided with a fan motor and any motor drive device describedabove, which drives, as a motor to be driven, the fan motor.

According to this embodiment, since the lock controller of theabovementioned motor drive device, in cases in which the control signalcontinues to instruct stoppage of rotation of the motor for thepredetermined first time-period or longer, has the lock protectioncircuit inactive, after rotation of the motor is stopped by aninstruction by the control signal, it is possible to promptly restartrotation of the motor, and to appropriately manage the temperature of adevice to be cooled.

An even further embodiment of the present invention is a lock protectionmethod. This method is a lock protection method of stopping energizationof a motor to be driven, when rotation of the motor is stopped, andincludes: monitoring a control signal which instructs rotation of themotor and measuring a time-period in which the control signal continuesto instruct stoppage of rotation of the motor; releasing lock protectionwhen the measured time-period exceeds a predetermined first time-period;and measuring a further predetermined second time-period on an occasionof the measured time-period reaching the first time-period, and afterthe second time-period has elapsed, transiting at least a part of amotor drive device to the standby mode.

According to this embodiment, since the lock protection is released whenthe control signal has instructed stoppage of rotation of the motor fora time-period exceeding the predetermined first time-period, after thecontrol signal has instructed stoppage of the motor, it is possible topromptly restart rotation of the motor and also to reduce powerconsumption.

It is to be noted that any arbitrary combination or rearrangement of theabove-described structural components and so forth is effective as andencompassed by the present embodiments.

Moreover, this summary of the invention does not necessarily describeall necessary features so that the invention may also be asub-combination of these described features.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, withreference to the accompanying drawings which are meant to be exemplary,not limiting, and wherein like elements are numbered alike in severalFigures, in which:

FIG. 1 is a circuit diagram showing a configuration of a cooling systemaccording to an embodiment;

FIG. 2 is a timing chart showing a drive restarting operation of a fanmotor in the cooling system of FIG. 1; and

FIG. 3 is a circuit diagram showing a configuration of a drive unitaccording to a modified example.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described based on preferred embodiments whichdo not intend to limit the scope of the present invention but exemplifythe invention. All of the features and the combinations thereofdescribed in the embodiment are not necessarily essential to theinvention.

An embodiment relates to a cooling system which blows cool air by a fan,on an object to be cooled, such as, for example, an LSI or the like.

FIG. 1 shows a configuration of the cooling system 200 according to theembodiment.

The cooling system 200 is provided with a motor drive device 100, a fanmotor 112, and a Hall element 114.

The fan motor 112 is a single-phase full-wave motor, and is arrangedopposite the object to be cooled, which is not shown in the figure. Inthe fan motor 112, a coil current, that is, an energization state, iscontrolled by a drive voltage outputted from the motor drive device 100,and rotation is controlled.

A first terminal of the Hall element 114 is connected to a power supplyline, to which a Hall bias voltage HB is applied, via a resistor R12,and a second terminal thereof is grounded via a resistor R11. Size of asignal outputted from the Hall element 114 is adjusted by the resistorR12 and the resistor R11. Therefore, either one or both of the resistorR11 and the resistor R12 may be shorted, according to an in-phase inputrange of a hysteresis comparator 22 described later. Furthermore, theHall bias voltage HB is generated by the motor drive device 100.

The Hall element 114 outputs a first Hall signal VH1 and a second Hallsignal VH2, whose level changes in accordance with position of a rotorof the fan motor 112. When the fan motor 112 rotates, the first Hallsignal VH1 and the second Hall signal VH2 are of mutually oppositephases, and a period is a sine wave that varies according to rotationalfrequency of the fan motor 112.

The motor drive device 100 drives the fan motor 112, based on the firstHall signal VH1, the second Hall signal VH2, and a control signal Vcnt.The motor drive device 100 is provided with a function that, whenstoppage of the fan motor 112 is instructed for a predetermined time orlonger by the control signal Vcnt, to be described later, cancels (makesinactive) a lock protection function which stops energization of the fanmotor 112. Furthermore, it is desirable that the motor drive device 100is a function IC monolithically integrated on one semiconductorsubstrate.

The motor drive device 100 has, as terminals for input and output ofsignals, a first input terminal 102, a second input terminal 104, acontrol input terminal 106, a first output terminal 108, a second outputterminal 110, and a Hall bias terminal 111.

The first Hall signal VH1 and the second Hall signal VH2 outputted bythe Hall element 114 are inputted to the first input terminal 102 andthe second input terminal 104.

The control signal Vcnt, instructing rotation of the fan motor 112 fromoutside, is inputted to the control input terminal 106.

A first drive voltage Vdr1 and a second drive voltage Vdr2, which drivethe fan motor 112, are respectively outputted from the first outputterminal 108 and the second output terminal 110.

The motor drive device 100 principally includes a drive unit 10, aprotection circuit 12, a PWM (Pulse Width Modulation) circuit 14, astandby controller 20, a voltage source 30, and a starting circuit 31.

The PWM circuit 14 generates a PWM signal Vpwm based on the controlsignal Vcnt inputted from outside. The generated PWM signal Vpwm isinputted to a pre-drive circuit 24, described later. The PWM circuit 14includes an oscillator 52 and a comparator 54.

The oscillator 52 generates, for example, a triangular waveform, asawtooth waveform, or the like. Oscillation frequency is preferablysufficiently larger than rotational frequency of the fan motor 112. Thecomparator 54 compares an output voltage Vosc of the oscillator 52 andthe control signal Vcnt, and outputs the PWM signal Vpwm at a high levelwhen Vcnt>Vosc and at a low level when Vcnt<Vosc. When the rotationalfrequency of the fan motor 112 is raised, the control signal Vcnt ispreferably enlarged and a duty ratio of the PWM signal Vpwm ispreferably enlarged. When the rotational frequency of the fan motor 112is lowered, the control signal Vcnt is preferably made smaller and theduty ratio of the PWM signal Vpwm is preferably made smaller. When thefan motor 112 is stopped, the control signal Vcnt is preferably madeeven smaller and on-duty of the PWM signal Vpwm is preferably got ridof.

The drive unit 10 drives the fan motor 112, based on the first Hallsignal VH1, the second Hall signal VH2, and the PWM signal Vpwmdescribed later.

The drive unit 10 includes the hysteresis comparator 22, the pre-drivecircuit 24, a H-bridge 26, and switches SW1 to SW4.

The hysteresis comparator 22 compares the first Hall signal VH1, thesecond Hall signal VH2 outputted from the Hall element 114, and outputsa rectangular waveform signal Vrct at a high level when VH1>VH2, and ata low level when VH1<VH2.

The pre-drive circuit 24 controls ON-OFF states of each switch making upthe H-bridge 26, based on the rectangular waveform signal Vrct outputtedfrom the hysteresis comparator 22 and the PWM signal Vpwm outputted fromthe PWM circuit 14.

The H-bridge 26 supplies the first drive voltage Vdr1 and the seconddrive voltage Vdr2 to the fan motor 112 by control by the pre-drivecircuit 24. The H-bridge 26 includes a first high side switch MH1, asecond high side switch MH2, a first low side switch ML1, and a secondlow side switch ML2.

The first high side switch MH1 and the second high side switch MH2 areP-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors),and the first low side switch ML1 and the second low side switch ML2 areN-channel MOSFETs.

The first high side switch MH1 and the first low side switch ML1 areconnected in series between a power line to which a power supply voltageVdd is applied, and ground. Voltage at a connection point of the firsthigh side switch MH1 and the first low side switch ML1 is applied to oneend of the fan motor 112 as the first drive voltage Vdr1, via the firstoutput terminal 108.

ON-OFF states of the first high side switch MH1 and the first low sideswitch ML1 are controlled by gate control signals SH1 and SL1 inputtedto each gate. That is, the first high side switch MH1 is ON when thegate control signal SH1 has a low level, and is OFF when the gatecontrol signal SH1 has a high level. Furthermore, the first low sideswitch ML1 is ON when the gate control signal SL1 has a high level, andis OFF when the gate control signal SL1 has a low level.

The first drive voltage Vdr1 applied to the fan motor 112 is the powersupply voltage Vdd when the first high side switch MH1 is ON and thefirst low side switch ML1 is OFF, and is ground potential OV when thefirst high side switch MH1 is OFF and the first low side switch ML1 isON.

In the same way, the second high side switch MH2 and the second low sideswitch ML2 are connected in series between a power line and ground.Voltage of a connection point of the second high side switch MH2 and thesecond low side switch ML2 is applied to the other end of the fan motor112 as the second drive voltage Vdr2, via the second output terminal110.

The protection circuit 12 controls ON-OFF states of each switch of theH-bridge 26 by the pre-drive circuit 24, based on the rectangularwaveform signal Vrct outputted from the hysteresis comparator 22 and thePWM signal Vpwm outputted from the PWM circuit 14.

Operation of the protection circuit 12 can be divided into two cases asbelow.

The first is the case in which the rectangular waveform signal Vrctceases to fluctuate in spite of the PWM signal Vpwm repeating a highlevel and a low level, that is, the case in which the fan motor 112 islocked by a force beyond its control, such as a foreign object beingcaught therein, or the like. In this case, the protection circuit 12instructs stoppage of energization of the fan motor 112, to thepre-drive circuit 24. In this way, excess current in the motor coil isprevented.

The other is the case in which the PWM signal Vpwm indicates a low levelfor a predetermined time-period or longer, that is, the case in whichthe fan motor 112 is intentionally stopped. In this case, differently tothe abovementioned case, the protection circuit 12 does not instructstoppage of energization of the fan motor 112 even if the rectangularwaveform signal Vrct does not fluctuate. In this way, a restartingoperation after the fan motor 112 has been intentionally stopped iscarried out smoothly.

The protection circuit 12 includes a lock protection circuit 32 and alock controller 34. Furthermore, a TSD (Thermal Shut Down) circuit orthe like may additionally be included.

The lock protection circuit 32 is active when an enable signal EN,described later, has a high level (i.e. asserted), and is inactive whenthe enable signal EN has a low level (i.e. negated).

When active, the lock protection circuit 32 detects that the fan motor112 is stopped by, for example, monitoring the rectangular waveformsignal Vrct outputted from the hysteresis comparator 22. When the lockprotection circuit 32 detects that the fan motor 112 is locked, itswitches a stop signal Vstop outputted to the pre-drive circuit 24 froma low level to a high level. When the stop signal Vstop switches to ahigh level, the pre-drive circuit 24 turns OFF all transistors MH1, MH2,ML1, and ML2, that make up the H-bridge 26. A time-period for turning aswitch OFF is preferably from a few hundred ms to a few seconds. Turningtransistors OFF may be performed by turning the switches SW1 to SW4,described later, ON. When energization is stopped by the stop signalVstop, a current is not supplied to the fan motor 112 even if the PWMsignal Vpwm is generated.

In this way, excess current is prevented from flowing when the fan motor112 is locked. Furthermore, a verification time-period is set from whenthe fan motor 112 stops until stoppage thereof is confirmed by the lockprotection circuit 32. The verification time-period is, for example,approximately 0.5 seconds, and is appropriately decided according to aninternal configuration of the lock protection circuit 32.

On the other hand, when inactive, the lock protection circuit 32consistently outputs the stop signal Vstop at a low level to thepre-drive circuit 24.

When the PWM signal Vpwm generated in the PWM circuit indicates a lowlevel for a time-period exceeding a predetermined time-period, the lockcontroller 34 has the lock protection circuit 32 inactive. Thepredetermined time-period may be sufficiently longer than a period ofthe PWM signal Vpwm, and may be shorter than the verificationtime-period until locking of the fan motor 112 is confirmed in the lockprotection circuit 32. The predetermined time-period is set at 60 ms inthe embodiment. This 60 ms is a time set based on an off-dutytime-period for an assumed lower limit frequency of the PWM signal Vpwm.

The lock controller 34 includes a counter 36 and a clock generator 38.

The clock generator 38 generates a clock of a predetermined frequency.The predetermined frequency can be appropriately decided to suit theabovementioned set predetermined time-period. The counter 36 counts thenumber of clocks generated in the clock generator 38, while the PWMsignal Vpwm outputted from the comparator 54 indicates a low level. Thatis, the counter 36 starts a count, with a count value at anegative-going edge of the PWM signal Vpwm being reset, and counts theclock until the PWM signal Vpwm is reset again at a negative-going edge.In counting, when it is detected that the PWM signal Vpwm exceeds theabovementioned predetermined time-period and indicates a low level, thecounter 36 switches the enable signal EN from a high level to a lowlevel, and outputs to the lock protection circuit 32.

The lock protection circuit 32 becomes inactive when the enable signalEN switches to a low level, and the stop signal Vstop outputted to thepre-drive circuit 24 is held at a low level. At this time, from the PWMsignal Vpwm continuously indicating a low level, since the pre-drivecircuit 24 controls each switch that makes up the H-bridge 26 to be OFF,even if the stop signal Vstop is at a low level, the fan motor 112 isnot energized.

Furthermore, the lock protection circuit 32 that was made inactive bythe enable signal EN switching to a low level becomes active againthereafter, when the PWM signal Vpwm has a high level.

The standby controller 20 receives the enable signal EN. The standbycontroller 20 starts time measurement, when the enable signal ENtransits from a high level to a low level. Here, the enable signal ENtransiting from a high level to a low level means that the controlsignal Vcnt is continuously instructing stoppage of the fan motor 112for a first time-period τ1 or more.

In a state in which the PWM signal Vpwm is fixed at a low level, when apredetermined second time-period τ2 elapses from starting timemeasurement, the motor drive device 100 is set to standby mode,operation of at least a part of the motor drive device 100 is stopped,and power saving is realized. The standby controller 20, in the standbymode, has the standby signal STB at a high level. The standby signalSTB, in the standby mode and normal operation mode, is supplied to acircuit block executing different processing, and a circuit blockperforming shutdown in the standby mode. That is, when the PWM signalVpwm continuously maintains a low level for a time-period of (τ1+τ2),the standby controller 20 makes the motor drive device 100 transition tothe standby mode.

An explanation is given concerning standby processing.

The starting circuit 31 is a voltage source which generates a referencevoltage of the motor drive device 100. The standby controller 20, in thestandby mode, stops the starting circuit 31. Since a reference currentgenerated based on this reference voltage is shut off by the referencevoltage shutting down, supply of the reference current to each blockinside the motor drive device 100 is stopped, and low power consumptionis realized.

Furthermore, the motor drive device 100 includes a voltage source 30which generates the Hall bias voltage HB to be supplied to the Hallelement 114 via a Hall bias terminal 111. When the standby signal STBhas a high level, the voltage source 30 shuts down and stops supplyingvoltage to the Hall element 114. In this way, power consumption by theHall element 114, and the resistors R11 and R12 is reduced.

Furthermore, in the circuit of FIG. 1, the switches SW1 to SW4 areprovided between gate and source of each transistor of the H-bridge 26.ON and OFF states of the switches SW1 to SW4 are controlled in tandemwith the standby signal STB, and are ON in the standby mode. As aresult, each transistor of the H-bridge 26 is in a completely OFF state,and power consumption in the standby mode is further reduced.

In the standby mode, other unnecessary circuits are shut down.

Furthermore, the standby controller 20 receives the PWM signal Vpwm. Inthe standby mode, at an occasion when the control signal Vcnt instructsdriving of the fan motor 112, the standby controller 20 resets from thestandby mode to the normal mode. For example, the standby controller 20may perform resetting to the normal mode by monitoring an edge of thePWM signal Vpwm.

On resetting to the normal mode, the standby signal STB has a low level,and the starting circuit 31 starts, to generate the reference voltage.In this way, current is supplied to each block of the motor drive device100 and operation is restarted.

FIG. 2 is a timing chart showing a drive restarting operation of the fanmotor in the cooling system 200 of FIG. 1. The timing chart of FIG. 2shows, in order from above, the second Hall signal VH2, the PWM signalVpwm, the enable signal EN, the standby signal STB, consumed current Iccof the circuit, and the stop signal Vstop. Moreover, the same figureshows a vertical axis and a horizontal axis enlarged and contracted, asappropriate.

From time T0 to time T1, the PWM circuit 14 outputs the PWM signal Vpwmwith a duty ratio corresponding to the size of the control signal Vcnt.During this time, the fan motor 112 rotates at a speed corresponding tothe duty ratio of the PWM signal Vpwm, and the second Hall signal VH2shows a sine wave of a frequency corresponding to the rotationalfrequency of the fan motor 112. Furthermore, in this time, since the PWMsignal Vpwm repeats a high level and a low level in a short time, theenable signal EN indicates a high level. Therefore, the lock protectioncircuit 32 is active. Furthermore, since the fan motor 112 is notstopped, the stop signal Vstop outputted from the lock protectioncircuit 32 to the pre-drive circuit 24 has a low level. Therefore, thepre-drive circuit 24 supplies the first drive voltage Vdr1 and thesecond drive voltage Vdr2 to the fan motor 112 by controlling ON-OFFstates of each switch of the H-bridge 26.

At time T1, when the control signal Vcnt is decreased in order to stopdriving of the fan motor 112, the duty ratio of the PWM signal Vpwm is0. After time T1, the PWM signal Vpwm has a low level until the controlsignal Vcnt is raised in order to restart driving of the fan motor 112at time T4.

The counter 36 counts the number of clocks generated in the clockgenerator 38, from time T1 at which the duty ratio of the PWM signalVpwm is 0, and at time T2 at which the predetermined first time-periodτ1 (=60 ms) has elapsed, the enable signal EN is switched from a highlevel to a low level. In this way, the lock protection circuit 32 isinactive.

In order to clarify a first effect of this embodiment, an explanationwill be given of operation in cases of performing switching of the lockprotection circuit 32 between being active and inactive by the enablesignal EN.

In such cases, rotation of the fan motor 112 is stopped by the dutyratio of the PWM signal being 0, and the Hall signal VH2 is fixed attime T1. If the Hall signal VH2 or the rectangular waveform signal Vrctcontinuously maintains a fixed value during a predetermined verificationtime-period τ3 (for example, 0.5 s), the lock protection circuit 32judges that the fan motor 112 is locked. In other words, theverification time-period τ3 is the time required for the lock protectioncircuit 32 to confirm that the fan motor 112 is stopped. If the lockprotection circuit 32 is active, at time T5 after the verificationtime-period τ3 has elapsed from time T1, the stop signal Vstop outputtedto the pre-drive circuit 24 is switched to a high level. The waveform atthis time is shown by an alternate long and short dash line. When thestop signal Vstop has a high level, energization of the fan motor 112 isstopped for a few seconds. Thus, at time T4, the level of the controlsignal Vcnt rises, and when rotation of the fan motor 112 is instructed,since the circuit is in a completely stopped state, starting of rotationof the fan motor 112 is delayed. For example, if rotation of the fanmotor 112 is instructed by the control signal Vcnt immediately after thestop signal Vstop has a high level, since there is no energization for afew seconds thereafter, rotation of the fan motor 112 is delayed.

In response to this, in the present embodiment, the lock protectioncircuit 32 is switched between being active and inactive by the enablesignal EN. That is, at time T1 the PWM signal Vpwm is set to a lowlevel, and at time T2 when the first time-period τ1 has elapsedthereafter, the enable signal EN is set to a low level. As a result, thelock protection circuit 32 is in an inactive state. When the lockprotection circuit 32 is in an inactive state, at time T5 also, at whichthe Hall signal VH2 has maintained a constant value for the verificationtime-period τ3, the stop signal Vstop, outputted to the pre-drivecircuit 24, does not switch to a high level and maintains a low level.

At time T4, the control signal Vcnt is raised to drive the fan motor 112once again. Thereupon, the PWM circuit 14 restarts output of the PWMsignal Vpwm with a duty ratio corresponding to the size of the controlsignal Vcnt. At this time, since the lock protection circuit 32 is madeinactive by the enable signal EN that is at a low level as describedabove, the lock controller 34 maintains the stop signal Vstop at a lowlevel. Therefore, when the control signal Vcnt is raised at time T4,driving of the fan motor 112 is promptly restarted, and the second Hallsignal VH2 indicates a sine wave.

At described above, according to the cooling system 200 of the presentembodiment, when the PWM signal Vpwm generated by the PWM circuit 14indicates a low level for a time-period exceeding a predeterminedtime-period, since the lock controller 34 has the lock protectioncircuit 32 inactive, it is possible to distinguish between a stoppage ofthe motor due to the PWM signal Vpwm and locking of the motor due to aforce beyond its control. Therefore, after rotation of the fan motor 112is stopped by the PWM signal Vpwm, the motor drive device 100 promptlyrestarts rotation thereof, and a quick cooling effect can be obtainedfor cases such as, for example, when it is necessary to rapidly cool adevice while the fan motor 112 is stopped.

Cases in which a function of the lock controller 34 is not provideddiffer from cases in which the function of the abovementioned lockcontroller 34 is provided. That is, when the function of the lockcontroller 34 is provided, the stop signal Vstop is maintained at a lowlevel also at time T5, but when this function is not provided, the stopsignal Vstop is switched to a high level at time T5. Therefore, when thefunction of the lock controller 34 is not provided, even if the controlsignal Vcnt for restarting driving of the fan motor 112 at time T4 israised, and input of the PWM signal Vpwm with a corresponding duty ratiois received, the pre-drive circuit 24 continues to have each switch ofthe H-bridge 26 OFF. As a result, the fan motor 112 is not energized,and driving cannot be promptly restarted. Thus, the temperature of adevice to be cooled cannot be appropriately managed.

According to the cooling system 200 according to the present embodiment,this type of problem can be preferably solved.

Next, a second effect of the embodiment is explained. When the enablesignal EN is switched to a low level at time T2, the standby controller20 starts time measurement in a time-period in which the PWM signal Vpwmhas a low level. When the time-period in which the PWM signal Vpwm has alow level is maintained for the second time-period τ2, the standbysignal STB is switched to a high level, and operation of each block ofthe motor drive device 100 is stopped. As a result, the circuit currentIcc of the motor drive device 100 decreases to the vicinity of 0 mA, andlow power consumption is realized.

After that, at time T4 when the PWM signal Vpwm goes to a high level,the standby controller 20 switches the standby signal STB to a lowlevel, and resets each block of the motor drive device 100 to a drivestate. If the PWM signal Vpwm has a high level before the secondtime-period has τ2 elapsed, there is no transition to the standby mode,and rotation of the fan motor 112 is restarted.

Moreover, according to setting of the counter 36, τ2≧0 is also feasible.

In this way, according to the motor drive device 100 according to thepresent embodiment, when a state in which rotation of the fan motor 112is not instructed is maintained for a predetermined time-period (τ1+τ2),by switching to the standby mode, it is possible to reduce currentconsumed in the circuit compared to conventional cases. In addition,since a transition to the standby mode of time T3 to T4 is executedbased on the enable signal EN, when transitioning to the standby mode,the function of the lock protection circuit 32 is guaranteed to bedisabled. Therefore, when restarting of rotation of the fan motor 112 isinstructed thereafter at time T4, it is possible to promptly reset fromthe standby mode to the normal mode and make the fan motor 112 rotate.

The abovementioned embodiment is an example, and a person skilled in theart will understand that various modifications in combinations ofvarious component elements and various processes thereof are possible,and that such modified examples are within the scope of the presentinvention.

In the embodiment, the drive unit 10 is formed of the hysteresiscomparator 22, the pre-drive circuit 24, and the H-bridge 26, but thepresent invention is not limited thereto.

FIG. 3 shows a configuration of a drive unit 60 according to a modifiedexample. The drive unit 60 includes a first operational amplifier 62 anda second operational amplifier 64.

A first drive voltage Vdr1 outputted by the first operational amplifier62 is fed back to an inverting input terminal of the first operationalamplifier 62 and a non-inverting input terminal of the secondoperational amplifier 64 by a resistor R16. A second drive voltage Vdr2outputted by the second operational amplifier 64 is fed back to anon-inverting input terminal of the first operational amplifier 62 andan inverting input terminal of the second operational amplifier 64 by aresistor R26.

The first operational amplifier 62 and the second operational amplifier64 are configured such that, at output stages, two transistors arearranged, connected in series between a power supply and ground, and anoutput voltage is taken from a connection point thereof. The twotransistors respectively arranged at output stages of the firstoperational amplifier 62 and the second operational amplifier 64correspond to the various switches in the H-bridge 26 of FIG. 1. Thefirst drive voltage Vrd1 and the second drive voltage Vdr2 have a valuethat is the difference between the first Hall signal VH1 and the secondHall signal VH2, which is amplified. Furthermore, when the lockprotection circuit 32 of FIG. 1 detects locking of the fan motor 112,and switches the stop signal Vstop from a low level to a high level, thefirst operational amplifier 62 and the second operational amplifier 64are OFF and energization of the fan motor 112 is stopped.

In the embodiment an explanation has been given concerning cases inwhich the PWM signal Vpwm is generated based on the control signal Vcnt,but the PWM signal Vpwm may be inputted directly from outside.

Furthermore, in the embodiment an explanation has been given of cases inwhich the motor drive device 100 performs PWM-driving of the fan motor112, but the present invention is not limited thereto. The motor drivedevice 100 may also perform linear driving of the fan motor 112.

Furthermore, in the embodiment an explanation has been given of cases inwhich the fan motor 112 is a single-phase motor, but the presentinvention is not limited thereto. The fan motor 112 may be a multi-phasemotor.

Furthermore, in the embodiment, rotation of the fan motor 112 isdetected by a Hall element 114, but the present invention is not limitedthereto. Rotation of the fan motor 112 may be detected by monitoringinduced voltage generated in a coil of the fan motor 112.

Furthermore, in the embodiment the lock controller 34 monitors time inwhich the PWM signal Vpwm indicates a low level, by the counter 36counting clocks generated by the clock generator 38, but the presentinvention is not limited thereto. The time in which the PWM signal Vpwmindicates a low level may be monitored by a time constant circuit thatuses a capacitor and a resistor to give a delay to the PWM signal Vpwm.

In the embodiment the lock protection circuit 32 monitors therectangular waveform signal Vrct, but the present invention is notlimited thereto. The lock protection circuit 32 may monitor the firstHall signal VH1 or the second Hall signal VH2, and may monitor inducedvoltage generated in the coil of the fan motor 112.

In the embodiment, an explanation has been given of cases in which themotor drive device 100 is monolithically integrated on one LSI, but thepresent invention is not limited thereto, and some of the componentelements may be arranged as discrete elements outside of the LSI or aschip parts, or may be configured as a plurality of LSIs. For example,the H-bridge 26 may be configured using a discrete power transistor.Furthermore, the clock generator 38 may be arranged externally, and thecounter 36 may count the clocks inputted from outside.

While the preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the appendedclaims.

1. A motor drive device comprising: an Hall element; a control inputterminal configured to receive a control signal instructing rotation ofa motor to be driven, the control signal being variable between a stateto instruct stoppage of the motor and a state to instruct driving of themotor; a pulse width modulator configured to generate a PWM signal basedon the control signal from the control input terminal and a signal froman oscillator; a drive unit configured to control energization of themotor based on a signal from the Hall element and the PWM signal; a lockprotection circuit configured to monitor a signal indicating a presentrotational condition of the motor and to stop energization of the motor,when rotation of the motor is stopped; a lock controller configured tohave the lock protection circuit inactive, in cases in which the controlsignal continues to instruct stoppage of the motor for at least apredetermined first time-period, the predetermined first time-periodbeing measured from a time at which the control signal transitions fromthe state to instruct driving of the motor to the state to instructstoppage of the motor; and a standby controller configured to start timemeasurement at an occasion when the control signal has continued toinstruct stoppage of the motor for at least the first time-period, andafter a further predetermined second time-period has elapsed, to stop atleast part of the motor drive device, and to make the motor drive devicetransit to a standby mode.
 2. A motor drive device according to claim 1,wherein the standby controller, in the standby mode, stops a voltagesource generating a reference voltage for the motor drive device.
 3. Amotor drive device according to claim 1, wherein the standby controller,in the standby mode, stops supplying of voltage to the Hall element. 4.A motor drive device according to claim 1, wherein the signal indicatinga present rotational condition of the motor is based on a signal from aback electromotive force induced at a coil of the motor.
 5. A motordrive device according to claim 1, wherein the standby controller, inthe standby mode, fixes electrical potential of a control terminal of atransistor of an output stage connected to a coil of the motor, to turnthe transistor fully OFF.
 6. A motor drive device according to claim 1,wherein the standby controller, at an occasion when the control signalinstructs driving of the motor, resets from the standby mode to normalmode.
 7. A motor drive device according to claim 1, wherein the motordrive device is monolithically integrated on one semiconductorsubstrate.
 8. A cooling system comprising: a fan motor; and a motordrive device configured to drive, as the motor to be driven, the fanmotor, the motor drive device comprising: an Hall element configured todetect rotation of a motor to be driven; a control input terminalconfigured to receive a control signal instructing rotation of themotor, the control signal being variable between a state to instructstoppage of the motor and a state to instruct driving of the motor; apulse width modulator configured to generate a PWM signal based on thecontrol signal from the control input terminal and a signal from anoscillator; a drive unit configured to control energization of the motorbased on a signal from the Hall element and the PWM signal; a lockprotection circuit configured to monitor a signal indicating a presentrotational condition of the motor and to stop energization of the motor,when rotation of the motor is stopped; a lock controller configured tohave the lock protection circuit inactive, in cases in which the controlsignal continues to instruct stoppage of the motor for at least apredetermined first time-period, the predetermined first time-periodbeing measured from a time at which the control signal transitions fromthe state to instruct driving of the motor to the state to instructstoppage of the motor; and a standby controller configured to start timemeasurement at an occasion when the control signal has continued toinstruct stoppage of the motor for at least the first time-period, andafter a further predetermined second time-period has elapsed, to stop atleast part of the motor drive device, and to make the motor drive devicetransit to a standby mode.
 9. A motor drive device comprising: an Hallelement configured to detect rotation of a motor to be driven; a controlinput terminal configured to receive a control signal instructingrotation of the motor, the control signal being variable between a stateto instruct stoppage of the motor and a state to instruct driving of themotor; a pulse width modulator configured to generate a PWM signal basedon the control signal from the control input terminal and a signal froman oscillator; a drive unit configured to control energization of themotor based on a signal from the Hall element and the PWM signal; a lockprotection circuit configured to monitor a signal indicating a presentrotational condition of the motor and to stop energization of the motor,when rotation of the motor is stopped; and a lock controller configuredto have the lock protection circuit inactive, in cases in which thecontrol signal continues to instruct stoppage of the motor for at leasta predetermined first time-period, the predetermined first time-periodbeing measured from a time at which the control signal transitions fromthe state to instruct driving of the motor to the state to instructstoppage of the motor, wherein the motor drive device starts timemeasurement at an occasion when the control signal has continued toinstruct stoppage of the motor for at least the first time-period, andafter a further predetermined second time-period has elapsed, the motordrive device makes transition to a standby mode.
 10. A motor drivedevice according to claim 9, wherein the standby controller, in thestandby mode, stops a voltage source generating a reference voltage forthe motor drive device.
 11. A motor drive device according to claim 9,wherein the signal indicating a present rotational condition of themotor is based on a signal from a Hall element for detecting rotation ofthe motor.
 12. A motor drive device according to claim 11, wherein thestandby controller, in the standby mode, stops supplying of voltage tothe Hall element.
 13. A motor drive device according to claim 9, whereinthe signal indicating a present rotational condition of the motor isbased on a signal from a back electromotive force induced at a coil ofthe motor.
 14. A motor drive device comprising: an Hall elementconfigured to detect rotation of a motor to be driven; a control inputterminal configured to receive a control signal instructing rotation ofthe motor, the control signal being variable between a state to instructstoppage of the motor and a state to instruct driving of the motor; apulse width modulator configured to generate a PWM signal based on thecontrol signal from the control input terminal and a signal from anoscillator; a drive unit configured to control energization of the motorbased on a signal from the Hall element and the PWM signal; a lockprotection circuit configured to monitor a signal indicating a presentrotational condition of the motor and to stop energization of the motor,when rotation of the motor is stopped; and a lock controller configuredto have the lock protection circuit inactive, in cases in which thecontrol signal continues to instruct stoppage of the motor for at leasta predetermined first time-period, the predetermined first time-periodbeing measured from a time at which the control signal transitions fromthe state to instruct driving of the motor to the state to instructstoppage of the motor, wherein the motor drive device starts timemeasurement at an occasion when the control signal has continued toinstruct stoppage of the motor for at least the first time-period, andafter a further predetermined second time-period has elapsed, the motordrive device stops at least part of the motor drive device.
 15. A motordrive device according to claim 14, wherein the standby controller, inthe standby mode, stops a voltage source generating a reference voltagefor the motor drive device.
 16. A motor drive device according to claim14, wherein the standby controller, in the standby mode, stops supplyingof voltage to the Hall element.
 17. A motor drive device according toclaim 14, wherein the signal indicating a present rotational conditionof the motor is based on a signal from a back electromotive forceinduced at a coil of the motor.